Conventional hazard displays are used to reduce the risk of damage to vehicles, damage to property, personal injury, and loss of life. Such displays are often used by vehicle operators (e.g., aircraft pilots) and operators of supervisory equipment (e.g., air traffic controllers). Hazards to vehicular operation are diverse. Hazards to aircraft include collision with terrain, collision with other aircraft (traffic), and encountering adverse weather. Conventional airborne weather displays and aircraft terrain displays present information describing areas where hazards (also called potential threats) are located relative to the position of the host aircraft. U.S. Pat. No. 4,484,192 to Seitz et al., U.S. Pat. No. 4,825,381 to Bottorf et al., U.S. Pat. No. 5,049,886 to Seitz et al., U.S. Pat. No. 5,179,638 to Dawson et al., and U.S. Pat. No. 6,448,922 to Kelly describe conventional hazard displays used in aircraft. Certain of these displays have dual use configurations in that they are capable of displaying weather radar information in a first setting and terrain information in a second setting.
Conventional displays operate according to a scan mode. The scan mode may use either a polar coordinate system or a Cartesian coordinate system. In airborne weather radar systems (which may include terrain display capabilities) the updating of weather information correlates with a sweep of the radar beam through a range of azimuth positions about the host aircraft position. Weather information is updated along a radial scan line having an origin generally centrally located at the bottom of the displayed image and proceeding in an arc about the origin. This scan mode and its image are sometimes referred to as “rho-theta” or as a “rho-theta” image because information is updated at a distance from the origin (rho) on the radial scan line when the radial scan line arrives at an angle (theta) in the arc across the displayed image. Of course, the rho-theta image may be produced and refreshed by vector or raster scan techniques independent of the manner in which information is updated. When weather radar displays are used to display terrain information, the terrain information is conventionally updated using the rho-theta scan mode. This manner of updating was initially adopted to accommodate the signal interface to the weather radar system display. Conventional raster displays continue to use rho-theta scan mode regardless of whether the image describes weather hazards or terrain hazards.
The exemplary conventional weather and terrain hazard display 100 of FIG. 1 presents a displayed image updated using a rho-theta scan mode. Display 100 includes a screen 110 and control panel 130. The displayed image 124 presented on screen 110 includes indicia of tracked objects 120-122. Tracked objects 120-122 may correspond to weather, terrain, and/or traffic. A hazardous region 145 is distinguished in displayed image 124 from other information by, for example, distinct color (e.g., red or yellow), distinct texture, brightness, or symbology. The region 145 may be considered particularly hazardous due to the type, number, or density of individual hazards. Control panel 130 permits an operator to select weather or terrain hazard information (mode), adjust how bright the image appears in ambient lighting (brightness), and select the scale of the displayed image (range). In operation, displayed image 124 may include one or more range identifying lines (dashed), each to denote a distance relative to the origin of the displayed image (i.e., a planned position indicator using an aircraft symbol just above the origin). The distance corresponding to each range identifying line may be 25%, 50%, and 75% of the user selected range (e.g., 10 nm). Displayed image 124 also includes a rho-theta scan line 125 that indicates the portion of the image being updated. The scan line sweeps in a continuous 180° arc between points A and B clockwise (always starting at point A), counter clockwise (always starting at point B), or alternating (A to B, then B to A). The alternating rho-theta scan mode is also called “wiper” mode analogous to automobile windshield wiper motion. If the display uses vector technology for refreshing the displayed image, the scan line 125 also indicates the portion of the image being refreshed.
An alternative to rho-theta scan mode is based on a Cartesian coordinate system. Here, the scan line is either horizontal or vertical and sweeps as a line parallel to a Cartesian coordinate axis (e.g., x or y). This scan mode is sometimes referred to as Cartesian “curtain” scan mode. The image is sometimes referred to as a curtain image because the scan line is analogous to a theater curtain.
In yet another conventional scan mode, updates are made at random positions in the displayed image. This scan mode is called random scan mode herein.
In rho-theta or Cartesian coordinate systems, alternate scan modes include scan modes called “fan” modes where two scan lines move in a manner analogous to opening and/or closing an oriental fan. In a fan mode, the displayed image is updated using two scan lines that begin at a central point (e.g., point C in FIG. 1) in the displayed image and proceed to the extremities of the displayed image (e.g., points A and B in FIG. 1). A second update may begin at the same point (C) or may begin at the extremities (A and B) and move toward the center (C) of the displayed image. Updating and/or refreshing on a vector refresh display may quickly alternate between the positions of the two scan lines.
Conventional displays may permit an operator to select one scan mode (e.g., “clockwise”, “wiper”, “opening fan”) for the displayed image as a whole.
Conventional scan modes as discussed above delay the presentation of updated information by providing the same update rate to the displayed image as a whole. Consequently, it is not possible for an operator to determine a central point (e.g., central azimuth) of a hazard or the perimeter of a hazard until the entire region of the displayed image describing the hazard has been scanned. Conventional displayed images have a uniform resolution throughout. Consequently, time may be inappropriately spent updating, at a high resolution, a portion of the displayed image having comparatively little hazard information. Updated information may change the shape, bearing, and distance to a hazard as well as the status of a region (e.g., region 145 in FIG. 1). Delay in the presentation of information may delay an operator's awareness of a hazard’ and may reduce the time the operator has to avoid the hazard